Enhanced transposition cutoffs ETC is a cute idea: in a normal AlphaBeta search with a hashtable, you will be searching through all possible moves, and for every move you make, you do a hashtable lookup to see if you can return immediately. ETC takes this idea one step further: Before doing your recursive AlphaBeta call, you look up all possible successor positions of the current position. If you get a hashtable hit on one of these calls which gives you a return value > beta, you can immediately return without a search. The reason ETC helps is that in the normal AlphaBeta case, you generate a movelist, and let's assume that move number 5 would lead to a hashtable hit leading to a cutoff. Nevertheless, in the normal AlphaBeta framework, you will have to search through moves number 1 - 4, and only then do you find that move number 5 gives you a cutoff. This search is made unnecessary with the ETC lookup.

See also